Direct-viewing storage tube with character writing electron gun



2 Sheets-Sheet l H. M. SMITH DIRECT-VIEWING STORAGE TUBE WITH CHARACTERWRITING ELECTRON GUN Dec. 27, 1955 Filed oct. 23, 1953 ii lllll F11.

Dec. 27. 1955 H. M. SMITH 2,728,872

DIRECTVIEWING STORAGE TUBE WITH CHARACTER WRITING ELECTRON GUN Filedoct. 25, 1953 2 sheets-sheet 2 [h @um Q E A uw uns in@ Slm @l BY 4MM, W

DmECT-VIEWHNG STGRAGE TUBE WITH CHAR- ACTER WRITNG ELECTRON GUN Henry M.Smith, Pacific Palisades, Calif., assigner, by

mesne assignments, to Hughes Aircraft Company, a corporation of DelawareApplication ctober 23, 1953, Serial No. 387,984

7 Claims. (Cl. S15- 12) This invention relates to direct-viewing storagetubes and more particularly to a direct-viewing storage tubeincorporating apparatus for producing an electron beam with a crosssectional area having the configuration of a desired informationcharacter for writing the character directly on the storage surface ofthe tube in a single operation.

The storage tube of the present invention comprises means for producinga character writing electron beam, a gun for producing flood electrons,a viewing screen, and a foraminous storage screen disposed adjacent tothe viewing screen to control the flow of ilood electrons to the storagescreen. The character writing electron beam is produced by means whichinclude a matrix mask of all the information characters that it isdesired to reproduce. Further, an electron gun for producing an electronbeam of sufficient cross sectional area to cover one character of thematrix mask. Deilecting means are utilized to direct this electron beamthrough the aperture of the matrix mask having the configuration of thecharacter that it is desired to reproduce. In this manner, certainelectrons in the beam are intercepted so that the remaining crosssection of the beam has the shape of the desired character.

This electron beam is then directed by means of an electrostatic lensand deflecting means to the portion of the storage screen in registerwith the position on the viewing screen where it is desired to reproducethe character. The high energy electrons of the beam produce a positivecharge on the bombarded areas of the storage screen, which allows theood electrons to pass through to the viewing screen to produce acontinuous visual reproduction of the character thereon.

The character writing electron beam of the disclosed tube constitutes apartially intercepted beam which has a cross section conforming to theconguration of the area of the character being reproduced. This resultsin an electron beam of relatively low density, making a storage screenwith a fast writing speed desirable. A storage screen having thisfeature is incorporated in the tube of the present invention, and isdescribed in a copending application for patent Serial No. 299,363,entitled Method and Apparatus for Utilizing Electron Bombardment InducedSurface Conductivity, by Siegfried Hansen, tiled July l5, 1952. Astorage screen of this type comprises a contrast control grid with alayer of dielectric material disposed thereon, and a collector grid incontact with the dielectric material wherein a storage surface isprovided by the exposed surface of dielectric material. A potentialgradient is maintained from the storage surface to the collector grid toeffect charging of the storage surface by a means believed to be byelectron bombardment induced conductivity. That is, when an area of thestorage surface is bombarded by high energy electrons, a large number ofelectrons in the dielectric material are liberated from their molecularbonds and are attracted through the molecular matrix constituting thedielectric material to the collector grid by the potential gradient toproduce a positive charge on the storage surface.` In this manner, awriting speed ld States Patent ice is realized that is several timesfaster than possible with conventional secondary electron emissionstorage screens.

Apparatus capable of producing an electron beam having a cross sectionin the form of a desired character together with means for selectingdilferent characters is well known in the art. This apparatus, however,has normally been used in conventional cathode ray tubes with theresulting concomitant limitations. For example, if it is desired to readinformation directly from the viewingscreen of the tube, it would benecessary to repeatedly excite the screen with the same information inorder to obtain the persistence required. Also, if a photographic recordwere to be made, the sequential producing of each character with limitedpersistence would make it necessary for the lens of the camera to remainopen during the entire writing process. This long exposure would requirethat all extraneous sources of light be eliminated.

The tube of the present invention, on the other hand, has none of theselimitations. Information, once written on the screen of the storage tuberemains until removed. Thus, a photographic record of all theinformation on the viewing screen may be made with a single shortexposure and information could be read from the screen withoutsuccessively exciting the screen with the same information. In additionto these advantages, the storage screen of the aforementioned type iscapable of very fast writing speeds, making it particularly adaptablefor use with the character writing electron beam which inherently has acomparatively low electron density.

It is therefore an object of this invention to provide a cathode raydevice for producing a sequence of visual characters for desiredintervals of time, each character being produced by means of a discreteoperation with an electron beam.

Another object of this invention is to provide a directviewing storagetube incorporating apparatus for producing a character writing electronbeam.

Still another object of this invention is to provide a cathode ray tubedevice including a storage screen capable of fast writing speeds,together with apparatus for producing a character writing electron beam.

A further object of this invention is to provide a directviewing storagetube with apparatus for producing a character writing electron beamcomprising a matrix mask and an electrostatic lens for focusing thematrix mask on the storage screen of the tube.

A still further object of this invention is to provide a direct-viewingstorage tube with apparatus for producing a character writing electronbeam comprising a matrix mask and apparatus for directing the electronbeam to a desired portion on the storage screen including anelectrostatic lens for focusing the matrix mask on the storage screenwhereby successive paths of the electron beam cross. through a commonline, and electron beam dellecting means having a center of deflectionon said line.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connection with theaccompanying drawings in which an embodiment of the invention isillustrated by way of example. lt is to be expressly understood,however, that the drawings are for the purpose of illustration anddescription only, and are not intended as a definition of the limits ofthe invention.

Fig. l illustrates a sectional view of an embodiment of the disclosedtube;

Fig. 2 illustrates a plan view of the matrix mask in the apparatus forproducing the character writing electron beam;

Fig. 3 is a plan view of the storage screen in the tube of Fig. l; and

Fig. 4 is a schematic diagram on the operation of the lens system of thetube of Fig. 1.

Referring to Fig. l, there; is shown an embodiment of the presentinvention comprising an evacuated envelope 10' which in its enlargedright portion, asviewed in the figure, is a storage screen 12` and aeviewing screen 14. Facing the storage screen 12 in the left portion ofenvelope 10' as viewed in the gure', is a flood gun 16 and apparatus forproducing a character writing electron beam and directing it in adesired direction towards storage screen 12. This apparatus comprises anelectron gun :i8 for generating an electron beam, a matrix mask 20having apertures in the shape of the characters to be reproduced, andselection meansv 22. for directing the electron beam through theaperture corresponding to the character to be reproduced. Subsequent topenetrating an aperture of the matrix mask 20,. the electron. beamtraverses an electrostatic lens 24 and deflecting means 26 for directingit in the desired direction towards storage screen t2. Although amagnetic lens may be employed' inlieu of electrostatic lens 24, theelectrostatic lens is preferred in that it does not rotate the electronbeam.

Electron gun 1S, which. produces the initial writing beam of electrons,comprises a cathode 3b with a heating clement .32, an intensity grid 34,accelerating electrodes 36, 38 and a focusing electrode 37. Heatingelement 32, one side of which may be connected to cathode 30 as shown,is connected across. a source of potential such as a battery 40. Cathode30 is maintained at a potential of the order ot -3000 volts with respectto ground by means of a connection to the negative terminal of a battery42, the positive terminal of which is connected to ground. intensitygrid 34 is maintained at a suiciently negative quiescent potential withrespect to that of the cathode 39 so that the flow of stream electronsis entirely cut oft. This is accomplished by a battery 43, providing apotential of the order of 2000 Volts in series with a resistor d4connected between cathode 30 and grid 34.

When it is desired to cause the electron stream to flow, the potentialof intensity grid 34- is increased until it is only from 50 to 100volts` negative relative to the potential oi cathode 36. In the presentcase, this is accomplished by impressing a pulse of suitable amplitudegenerated by a pulse generator 45 on intensity grid 34 by means of aconnectionA thereto from pulse generator 4S through a capacitor 31. Theduration of the pulse is for the time necessary to Write one characteron the storage screen i2,

Electrodes 36, 37 andy 38 form an electrostatic lens system for focusingthe electron beam. Electrodes 36, 3S are maintained at apotential of theorder of 200 volts positive with respect to ground by means, of aconnection to a reference bus 39 which is maintained at the desiredpotential by suitable connections to a battery 41. An adjustablepotential of the. order of +800 volts relative to cathode 30 or -2200volts with respect to ground is maintained on electrode 37 for focusingthe electron beam. ri`his is accomplished by means of a connection fromythe electrode 37 to an adjustable tap 46 of a potentiometer 4"/ whichlis, in turn, connected across battery 42.

Selection means 22, for directing the electron stream through thcaperture corresponding to the character in matrix mask 20 to bereproduced, comprises vertical selection plates 43 and horizontalselection plates 49. Vertical and horizontal selection plates' 4d, 49are maintained at a quiescent potential of +200 volts with respect toground by means of a connection to reference bus 39 through isolationresistors t), 51' and 52, 53, respectively. Vertical selection plates 45are energized by a vertical voltage generator 55 connected acrossisolation resistors Sti, 51. Similarly,.horizontal. selection plates 49are energized by a horizontal voltage generator 54 connected acrossisolation resistors 52, 53'. A` control circuit 56, coupled to pulsegenerator 45 and generators 54, 55, is

provided to first determine the vertical and horizontal voltages to beproduced by generators 54, 55 in order to have selection means 22 directthe electron beam through the aperture corresponding to a desiredcharacter in matrix 29 and, secondly, to trigger pulse generator 45 tocause the electron stream to flow through the aperture for a period oftime required for the character to be written on the storage screen 12.It is preferred that there be no ilow of beam electrons when changingfrom one aperture to another in the matrix 20 and further, that theelectron beam does not dow for too long a period of time through asingle aperture because of the possibility of damage to the storagescreen 12.

The matrix mask 20, a plan view of which is shown in Fig. 2, comprises athin conductive electrode having an aperture in the shape of eachcharacter that it is desired to produce. Although the arrangement of thecharacters is entirely arbitrary, it is preferable that the most usedcharacters be disposed in the center region of the mask 20 in order thatminimum deflection of the electron beam be required to direct it throughthe apertures of those most used characters. The electron beam, ofcourse, must be of appropriate cross sectional area so as to completelycover only one aperture in the matrix at any one time. illustrated inFig. 2 is the matrix mask 20 with forty-five apertures shown by way ofexample. In the arrangement of characters shown, an E is disposed in thecenter position where an undeected electron beam would strike. Theremaining characters are disposed at equal increments of horizontal andvertical deflection away from the E, as shown.

Disposed about the path of the electron beam after it has penetratedthrough an aperture in the matrix mask 20 are the electrostatic lens 24and electron beam dellecting means 26. Lens 24 comprises annularelectrodes 59, 60 and 61, which are all of the same diameter anddisposed as shown in the ligure. Electrodes 59 and 61 are maintained atthe potential of 200 volts positive with respect to ground by means of aconnection to reference bus 39, while electrode 60 is maintained at anadjustable potential of the order of +1000 volts with respect to ground.This latter potential is impressed on electrode 6i) by means of aconnectionto an adjustable contact 64 of a potentiometer 65 which is, inturn, connected across a battery 66 which has its negative terminalconnected to ground. The function of lens 24 is to bring the matrix 2t)into focus at the storage screen 12 in such a manner that the electronbeam always crosses over at the centers of deection of electron beamdeflecting means 26. That is, the various paths of the electron beam,subsequent to passing through the apertures of matrix 20, would crossover at the centers of deflection of deecting means 26. .it is apparentthat the magnetic focusing, may also. be used to focus the matrix maskZtl on the storage screen l2, and is considered to be within the scopeof the present invention. A magnetic lens, however, as compared to theelectrostatic lens 24 used in this application, has the disadvantage ofcausing the electron beam to rotate. In a comparatively strong magneticeld, individual characters may even be distorted due to some portionsrotating more than others.

The electron beam deliecting means 26 comprise horizontal. deiiectionplates 68 and vertical deflection plates 70 disposed about the path ofthe electron beam, as shown. Horizontal and vertical deflection plates68, 70 are maintained at a quiescent potential of 200 volts positivewith respect to ground by means of connections to reference bus 39through isolation resistors 72, 73 and 74, 75, respectively. Horizontal.deflection plates 68 are energized by a horizontal deliection voltagegenerator 76 connected thereto across isolation resistors 72, 73 throughcapacitors 77, 78. Similarly, vertical deflection plates 70 areenergized by a vertical dellection voltage generator Si) connectedlthereto across isolation resistors 74, 75 through capacitors 81,82.

Flood gun 16', in conjunction with electrodes 95 and 96,

amasar;-

produces a broad beam of flood electrons that is directed uniformly overthe entire area of storage screen 12. Flood gun 16 is disposed adjacentto one of the vertical deflection plates 70, and comprises a cathode 90surrounded by an intensity grid 91 having a circular aperture in itscenter portion and annular electrodes 92 and 93 disposed in successionin front of and concentrically about the aperture in intensity grid 91.The cathode 90 is operated at ground potential by means of a connectionthereto while intensity grid 91 is maintained at a potential of theorder of 100 volts negative with respect to ground. The latter isaccomplished by means of a connection from intensity grid 91 to anadjustable tap 97 of a potentiometer 98, which is connected across abattery 100, an intermediate point of which is connected to ground sothat both positive and negative potentials are available frompotentiometer 93. Electrode 93 is maintained at a potential of the orderof +200 volts with respect to ground by means of a connection toreference bus 39 while electrode 92 is maintained at a potential of from150 to 200 volts positive with respect to ground, depending upon thedesired diameter of the beam of ilood electrons. This potential isapplied to electrode 92 by means of a connection thereto from a tap 99of potentiometer 98.

Electrodes 95 and 96 are disposed concentrically about the innerperiphery of envelope 10 in succession from vertical deilection plates70 to storage screen 12. These electrodes 95, 96 are composed of aconductive coating, which may be provided, for example, by painting theenvelope 10 with a colloidal solution of carbon such as AquadagElectrode 95 is maintained at a potential of the order of +200 voltswith respect to ground by means of a connection to reference bus 39.Electrode 96 is maintained at a potential of from 50 to 100 voltspositive with respect to ground by means of a connection to anadjustable tap 103 of a potentiometer 105 which is connected across abattery 106, an intermediate terminal of which is connected to ground.

Disposed in the enlarged portion of envelope 10 opposite to the ood gun16 and the apparatus for producing the character writing electron beamare the storage screen 12 and the viewing screen 14. Fig. l illustratesan enlarged cross sectional view of the storage screen 12 which isdisposed adjacent to and in front of the viewing screen 14 so that itmay control the ow of flood electrons thereto. Storage screen 12comprises a screen grid 110 which serves as a contrast control grid, athin at screen 112 with an annular electrode 113 about its periphery toprovide a collector grid, and a dielectricmaterial 114 disposed betweencontrast control grid 110 and the ilat screen 112 whereby the exposedportions of the surface of the dielectric material 114 provide a storagesurface. In accordance with the tentative theory of operation of thedevice, the dielectric material 114 used for this purpose must exhibitinduced conductivity and secondary electron emission characteristicswhen bombarded by electrons. An enlarged view of a portion of storagescreen 12 showing the contrast control grid 110, flat screen 112, anddielectric material 114, is illustrated in Fig. 3. As shown in thisfigure, one set of the parallel Wires constituting iiat screen 112 isdisposed at an angle of approximately 27.5 degrees relative to the sidesof the rectangular openings of grid 110 in order to avoid the formationof a moire pattern by the iiood electrons in passing through storagescreen 12.

A suitable material for contrast control grid 110, is, for example, anelectroformed 40 percent transparent nickel screen having 250 openingsper inch. The number of openings per inch, and other dimensions of thescreen used for making contrast control grid 110 is not especiallycritical, the primary consideration determining the above parametersbeing the ultimate transparency of the screen to electrons,.the eldpenetration required, and the ultimate definition desired. The contrastcontrol grid 110 is supported by a metal frame 116 which also serves asa mechanical support for the remaining elements of storage? screen 12.

Applied directly on the contrast control grid is dielectric material 114which provides the storage surface. Dielectric material 114 must have avery high specic resistance and, as previously mentioned, must exhibitinduced conductivity and secondary electron emission when subjected tobombardment by high energy incident electrons. The property of inducedconductivity of a normally nonconducting dielectric material is broughtabout because of the matrix structure of solid material. The moleculescomposing the material form a matrix structure which occupies only asmall fraction of its apparent volume. When bombarded by high energyelectrons, large numbers of electrons are freed from their molecularbonds to constitute electrons raised to the conduction band energylevel. These freed electrons are then attracted through the molecularmatrix of the material for a distance of the order of a fraction of amillimeter by means of a suitable potential gradient. A representativematerial that may be used for dielectric material 114 is, for example,talc.

Mounted in contact with the exposed surface of dielectric material 114is the ilat screen 112 which constitutes a thin flat metallic screen.This screen may be of an appropriate conducting material such as anevaporated aluminum, silver or gold mesh, having a thickness of theorder of l0 to 30 millionths of an inch, a pitch of 0.010 inch and ahole size of 0.008 inch by 0.008 inch. The exposed surface of thedielectric material 114 within the holes of flat screen 112 constitutesthe storage surface of the storage screen 12.

Contrast control grid 110 is maintained at an appropriate potential soas to regulate the ow of ood electrons through storage screen 12 toviewing screen 14. This potential may be of the order of -10 volts withrespect to ground, and is applied by means of a connection to anadjustable tap 104 of potentiometer 105. Flat screen 112 is maintainedat a potential of the order of 175 volts with respect to ground by meansof a connection to a tap 102 of potentiometer 105.

Viewing screen 14 is disposed adjacent to and behind` storage screen 12with respect to the electron beams. This screen is disposed on the innersurface at the end of the enlarged portion of envelope 10, and comprisesa conductive transparent layer and a thin fluorescent screen 122.Conductive transparent layer 120 is disposed directly on the glasssurface, and may be provided by a layer of stannous oxide. One method offorming this layer of stannous oxide on the glass is to expose it to theaction of stannous chloride in the presence of oxygen. Various otherviewing screen materials may be used, depending on the desiredcharacteristics. The construction of such viewing screen, however, isnot critical for the purposes of this invention. Conductive layer 120 ismaintained at a high positive potential so as to acceleratek electronspassing through the interstices of storage screen 12 to a suiiicientlyhigh velocity so that their kinetic energy will be converted to adesired amount of light at the time of impingement upon the viewingscreen. This potential is applied by means of a connection to thepositive terminal of a battery 124, the negative terminal of which isconnected to ground. The magnitude of the potential provided by battery124 may be of the order of from +5000 to -{-l0,000 volts.

In the operation of the character writing direct-viewing storage tube ofthe present invention, the horizontal and vertical Voltage generators54, 55, in response to control circuit 56, produce appropriate voltageswhich are impressed on selection plates 48, 49 for directing the path ofthe electron beam towards the aperture corresponding to the character inmatrix mask 20 that it is desired to write. The voltage applied toelectrode 37 of the lens system provided by electrodes 36, 37 and 38, isadjusted by means of tap 46 of potentiometer 47 so that the electronbeam has a cross sectional area at the matrix mask 20 to cover only onecomplete character. Upon passing through the matrix mask 20, beamelectrons not directed through' the aperture of the character to bewritten, are interceptedso that an electron beam is produced having across sectional area with the shape of the character.

After passing through the matrix mask 2i), the electron beam is directedto a predetermined portion or" the storage .screenI 12 by meansot theelectrostatic lens 24 and electron beam deilecting means 26. In order toexplain more clearly the preferred manner in which this effected,reference is made to Fig. 4. This ligure shows a schematic diagram ofthe matrix mask 2li, electrostatic lens 24 including electrodes S9, 6l!and 6i, vertical dcection plates 70 andy storage screen l2. Further,dashed lines 139 indicate equipotential surfaces of the electrostaticlens 24 and lines 132 represent successive paths of the electron beamwhen acted upon by the lens only. The electrostatic lens 24k ispreferably adjusted to focus the matrix mask 20 on theV storage screenl2 in such manner that successive paths 132 of the electron beam crossover at a common point 134 in the plane shown. lt is to be notedV thatthe velocity of the electron beam may be increased after it has passedthrough the matrix mask 20, if desired, in order. tominimize thedivergence of the successive paths 132 of the electron beam and thus aidin focusing the matrix mask 2G on the storage screen i2. This would alsoreduce the velocity at which the electrons are incident on the mask Ztl,thus considerably reducing the energy dissipated about the` edges of theapertures.

As shown in Fig. 4, the common point 13d is a distance a from the lens,and a distance b from the storage screen I2. With this being the case,the apertures of matrix 2b, focused on the storage screen l2, aremagnified by an' amount I'n order to greatly simplify the directing ofthe electronr beam to predetermined portions of the storage screen 12,the common point i3d should coincide with the center of deection of thevertical deflection plates 7l). In this event, compensating voltagesthat are directly proportional' to the deilecting potentials impressedon the deflecting plates d3 of selection means 22 may be applied todeflection plates 7i) so that the beam may be directed to apredetermined portion of storage screen 12, irrespective of thecharacter being presented.

Normally, the different distance of horizontal deiiection plates 49 fromthe lens 2li' will cause the successive paths 132 of the electron beamto cross over at points that form a locus which is spaced' from commonpoint i341 ln the vertical plane shown, the locus of these points isindicated' by a dashed line 3.36 in Fig. 4. When this is the case, thecenter of deflection of the horizontal deiiection plates 68 is made tofal on the line i3d. Horizontal and vertical deflection voltagegenerators 76, Sti generate voltages which are impressed on deflectionplates 68 and 70 to direct the electron beam to the particular portionof storage screen l2 on which it is desired to write the character.

ln ord'er to write on the storage screen, it is necessary to maintain apotential gradient from the storage surface to the iiat screen H2. Thisis effected by means of flood electrons produced by flood gun le. Floodelectrons are directed uniformly over the entire storage Isurface toliberate fewer secondary electrons than incident primary electrons. inthis manner, the storage surface is charged in a negative directionuntil it has reached the potential of the 'ood gun cathode 9?. Thus, apotential gradient is produced from the storage surface provided bydielectric material 1'l4' to the iiat screen H2.

When writing upon the storage surface, the character writing electronbeam bombards an area of storage surface having a shape similar to thatof the aperture in matrix mask 29 that it traversed. ln accordance withthe tentative theory of operation, the highenergy electrons of theelectron beameach liberate numerous additional electrons from theirmolecular bondsinI the molecular matrix comprising the dielectricmaterial H4 which provides the storage surface. These' electrons areattracted through this molecular matrix tox thetiat screen M2 to chargethe bombarded portion of the storage surface in a positive direction. Inorder for the charge to remain on the storage surface, it is necessarythat the initial charge effected by the writ-ing' beam be greater thanthe critical potential of the storage4 surface; The iioody electronsthen liberate more secondary electrons than incident primary electronsfrom the positive charged portions of the storage surface to` chargetheseportions to the potential of the flat screen- 112". The horizontal'and vertical deilection voltage generators 7e and 80J successively movethe electron beam from one portionto the next on the storage surface asthe vertical and horizontal selection voltage generators 55 and 54'directY the electron beam through the selected character apertures inthe matrix mask 20 to write the characters in sequence across thestorage screen l2.

A visual image of the positively charged areas on thc storage surface isthen produced on the viewing screen I4 by the action of the loodelectrons. The contrast control grid is maintained at a sufficientlynegative potential to prevent any field penetration from the highvoltage of the' viewing screen when the storage surface is at thepotential` of the ood gun cathode 9i), thus causing' the floodelectrons' toV be repelled. When there is a positive charge on thestorageV surface, however, the potential of contrast control grid' llt)Yis sufficiently positive so that there is iield penetration from theviewing screen through the storagev screenk 12, thereby enabling the oodelectrons to' penetrate through the interstices of the positive chargedareas of the storage surface and be accelerated towards the viewingscreen 14 to produce a visual image of the characters written on thestorage screen.

Thevisual' image of these characters may be maintained so long as thecollector grid' 112 is maintained at apotential of the order of twicethe critical potential of the storage surface material". When it isAdesired tol erase the characters constituting the positively chargedareas on the storage screen 12, it is only necessary to momentarilylower the potential ofthe fiat screen 112 to a potential that is lessthan the critical potential of the storage surface material and thenraise it gradually back to its original value. ln this event, thepotential' of the storage surface is returned to the potential of theflood gun cathode 90 by flood electrons, thereby creating apotentialgradient from the storage surface to the flat screen 112, thus makingthe storage screen 12 ready for wn'ting by the character writingelectron beam.

What is claimed as new is:

l. An electronic storage tube for thel visual presentation ofinformation characters, saidtube comprising a storage screen including aforaminous conductive element, a layer of dielectric material thatexhibits secondary electron emission' when bombarded by electronsdisposedv on said foraminous conductive element, said layer ofdielectric material' having arr exposed surface, and a flat conductivescreen disposed in contact with said exposed surface, the portions ofsaid exposed surface within the openings of said screen constituting astorage surface; means for producing an electronV beam; a matrix maskhaving a plurality of apertures, each of said apertures conforming to aninformation character; means for successively directing said electronbeam through the apertures conforming to characters to be presented tomake the cross sectional area of said electron beam successively conformto the configuration of each of the characters; means for maintainingsaid flat conducting screen at a first potential level; means formaintaining saidy storage surface at a second potential level negativewith respect to said first potential level to produce a positivepotential gradient from said storage surface to said at conductivescreen; means for successively directing said electron beam to bombardpredetermined portions of said storage screen to liberate numerouselectrons within the bombarded portions of said dielectric material foreach electron incident thereon whereby said liberated electrons areattracted to said at conductive screen by said potential gradient toproduce a series of charge replicas of the characters to be presented onsaid storage surface; and means responsive to said charge replicas forproducing a visual presentation of the information characters.

2. The electronic storage tube as defined in claim l wherein said meansfor successively directing said electron beam to bombard predeterminedportions of said storage screen includes apparatus for producing anelectrostatic lens for focusing said matrix mask on said storage screenwhereby successive paths of said electron beam, in traversing theapertures of said matrix mask, cross over at a predetermined distancefrom said matrix mask, and electron beam deflecting means having acenter of deflection at said predetermined distance from said matrixmask for directing said electron beam to said predetermined portions ofsaid storage screen.

3. An electronic storage tube for the visual presentation of informationcharacters, said tube Vcomprising means for producing an electron beam;a matrix mask having a plurality of apertures, each of said aperturesconforming to an information character; means for successively directingsaid electron beam through the apertures conforming to characters to bepresented to make the cross sectional area of said electron beamsuccessively conform to the configuration of each of the characters; astorage screen including a foraminous grid structure, a layer ofdielectric material that exhibits secondary electron emission andinduced conductivity when bombarded by electrons disposed on saidforaminous grid structure, said layer of dielectric material having anexposed surface, and a conductive screen disposed in contact with saidexposed surface, the portions of said exposed surface within theopenings of said screen constituting a storage surface; means formaintaining said conductive screen at a iirst potential level; means fordirecting Hood electrons emanating from a gun at a second potentiallevel, negative with respect to said iirst potential level, uniformlyover the area of said storage surface to charge each elemental areathereof substantially to said second potential level whereby a potentialgradient is produced from said storage surface to said conductivescreen; means for successively directing said electron beam to bombardpredetermined portions of said storage screen to produce numerousconduction electrons within the bombarded portions of said dielectricmaterial for each electron incident thereon whereby said conductionelectrons are attracted to said conductive screen by said potentialgradient to produce a series of charge replicas of the characters to bepresented on said storage surface; a viewing screen disposed contiguousto and in register with said storage screen on the side opposite fromsaid storage surface; and means for directing additional iiood electronsthrough the foramina of said storage surface contained within eachelemental area of said charge replicas in a collimated beam to saidviewing screen to produce a Visual presentation of said informationcharacters.

4. The electronic storage tube as defined in claim 3, wherein said meansfor successively directing said electron beam to bombard predeterminedportions of said storage screen includes means for producing anelectrostatic lens for focusing said matrix mask on said storage screenwhereby successive paths of said electron beam cross over at apredetermined distance from said mask, and electron beam deflectingmeans having a center of deflection at said predetermined distance fromsaid mask for directing said electron beam to said predetermined portionof said storage screen.

5. The electronic storage tube as defined in claim 3 wherein said firstpotential level is positive with respect to said second potential by anamount equal to twice the critical potential of said dielectric materialwhereby said flood electrons charge all areas of said storage surfaceinitially charged to at least the critical potential of said dielectricmaterial to said first potential level.

6. The electronic storage tube as defined in claim 3, including avoltage generator coupled to said conductive screen for lowering thepotential thereof from said first potential level to a potential lessthan the critical potential of said dielectric material and then togradually increase the potential of said conductive screen back to saidfirst potential level to erase said charge replicas from said storagesurface.

7. An electronic storage tube for the visual presentation of informationcharacters, said tube comprising a matrix mask having a plurality ofapertures, each of said apertures conforming to an informationcharacter; means for producing an electron beam; means for successivelydirecting said electron beam through selected apertures conforming tothe characters to be presented to make the transverse cross sectionalarea of said electron beam successively conform to the configuration ofthe selected characters, respectively; a storage screen; means includingapparatus for producing an electron lens to focus said matrix mask onsaid storage screen for successively directing said electron beam topredetermined portions of Y said storage screen to produce a series ofcharge replicas of the characters to be presented thereon; and meansresponsive to said charge replicas to produce a visual presentation ofthe information characters.

References Cited in the le of this patent UNITED STATES PATENTS

